addopt strict concurrency (#50)

* remove support for versions of Swift <= 5.6

* Simplify the Package.swift for older Swift versions

* bump swift version on example project 

* add StrictConcurrency to prepare for Swift 6with  StrictConcurrency=complete syntax

* use a computed property for dateformatter

* refine CloudwatchDetail for Sendable conformance

Author: sebsto

Package.swift

@@ -13,8 +13,10 @@ let package = Package(
     ],
     targets: [
         .target(name: "AWSLambdaEvents",
-                dependencies: [.product(name: "HTTPTypes", package: "swift-http-types")]),
+                dependencies: [.product(name: "HTTPTypes", package: "swift-http-types")],
+                swiftSettings: [.enableExperimentalFeature("StrictConcurrency=complete")]),
         .testTarget(name: "AWSLambdaEventsTests",
-                    dependencies: ["AWSLambdaEvents"]),
+                    dependencies: ["AWSLambdaEvents"],
+                    swiftSettings: [.enableExperimentalFeature("StrictConcurrency=complete")]),
     ]
 )

Sources/AWSLambdaEvents/AWSRegion.swift

@@ -25,7 +25,7 @@ public struct AWSRegion: RawRepresentable, Equatable {
         self.rawValue = rawValue
     }
 
-    static var all: [AWSRegion] = [
+    static let all: [AWSRegion] = [
         Self.af_south_1,
         Self.ap_northeast_1,
         Self.ap_northeast_2,

Sources/AWSLambdaEvents/Cloudwatch.swift

@@ -21,7 +21,7 @@ import struct Foundation.Date
 /// EventBridge has the same events/notification types as CloudWatch
 public typealias EventBridgeEvent = CloudwatchEvent
 
-public protocol CloudwatchDetail: Decodable {
+public protocol CloudwatchDetail: Decodable, Sendable {
     static var name: String { get }
 }
 
@@ -37,7 +37,8 @@ extension CloudwatchDetail {
 /// https://docs.aws.amazon.com/lambda/latest/dg/services-cloudwatchevents.html
 /// https://docs.aws.amazon.com/AmazonCloudWatch/latest/events/EventTypes.html
 /// https://docs.aws.amazon.com/eventbridge/latest/userguide/event-types.html
-public struct CloudwatchEvent<Detail: CloudwatchDetail>: Decodable {
+/// https://docs.aws.amazon.com/eventbridge/latest/userguide/eb-events-structure.html
+public struct CloudwatchEvent<Detail: CloudwatchDetail>: Decodable, Sendable {
     public let id: String
     public let source: String
     public let accountId: String
@@ -89,11 +90,11 @@ public enum CloudwatchDetails {
         public static let name = "Scheduled Event"
     }
 
-    public enum EC2 {
+    public enum EC2: Sendable {
         public struct InstanceStateChangeNotification: CloudwatchDetail {
             public static let name = "EC2 Instance State-change Notification"
 
-            public enum State: String, Codable {
+            public enum State: String, Codable, Sendable {
                 case running
                 case shuttingDown = "shutting-down"
                 case stopped
@@ -113,7 +114,7 @@ public enum CloudwatchDetails {
         public struct SpotInstanceInterruptionNotice: CloudwatchDetail {
             public static let name = "EC2 Spot Instance Interruption Warning"
 
-            public enum Action: String, Codable {
+            public enum Action: String, Codable, Sendable {
                 case hibernate
                 case stop
                 case terminate
@@ -131,12 +132,6 @@ public enum CloudwatchDetails {
 
     struct TypeMismatch: Error {
         let name: String
-        let type: Any
+        let type: any CloudwatchDetail.Type
     }
 }
-
-#if swift(>=5.6)
-extension CloudwatchEvent: Sendable where Detail: Sendable {}
-extension CloudwatchDetails.EC2: Sendable {}
-extension CloudwatchDetails.Scheduled: Sendable {}
-#endif

Sources/AWSLambdaEvents/Utils/DateWrappers.swift

@@ -39,9 +39,7 @@ public struct ISO8601Coding: Decodable {
         self.wrappedValue = date
     }
 
-    private static let dateFormatter: DateFormatter = Self.createDateFormatter()
-
-    private static func createDateFormatter() -> DateFormatter {
+    private static var dateFormatter: DateFormatter {
         let formatter = DateFormatter()
         formatter.locale = Locale(identifier: "en_US_POSIX")
         formatter.timeZone = TimeZone(secondsFromGMT: 0)
@@ -68,9 +66,7 @@ public struct ISO8601WithFractionalSecondsCoding: Decodable {
         self.wrappedValue = date
     }
 
-    private static let dateFormatter: DateFormatter = Self.createDateFormatter()
-
-    private static func createDateFormatter() -> DateFormatter {
+    private static var dateFormatter: DateFormatter {
         let formatter = DateFormatter()
         formatter.locale = Locale(identifier: "en_US_POSIX")
         formatter.timeZone = TimeZone(secondsFromGMT: 0)
@@ -105,8 +101,7 @@ public struct RFC5322DateTimeCoding: Decodable {
             "Expected date to be in RFC5322 date-time format, but `\(string)` is not in the correct format")
     }
 
-    private static let dateFormatters: [DateFormatter] = Self.createDateFormatters()
-    private static func createDateFormatters() -> [DateFormatter] {
+    private static var dateFormatters: [DateFormatter] {
         // rfc5322 dates received in SES mails sometimes do not include the day, so need two dateformatters
         // one with a day and one without
         let formatterWithDay = DateFormatter()